This invention relates generally to laser windows, and, more particularly, to a high energy rotating laser window suspended by a gas bearing.
Since the development of the first working lasers, considerable time and effort has been expended in the search for higher output laser systems. The possible applications of high power lasers are unlimited in the fields of communication, manufacturing, construction, medicine, space exploration and defense. Unfortunately many obstacles exist to the attainment of high power systems. One such obstacle is found in the utilization of conventional laser windows.
A high-power laser system requires one or more windows to maintain separation of the fluids in the optical cavity from the external environment while allowing the unobstructed transmission of the intense electromagnetic radiation beam. This presents a design problem because the transparency of existing materials to the laser radiation wave lengths is less than perfect and even a very low percentage absorption of the beam will, in a few seconds, produce temperature gradients and deformations which cause unacceptable optical distortions or potentially excessive thermal stresses.
Apertures which physically separate the lasing media from the ambient while allowing the transmission of the desired electromagnetic excitation produced by the device are fundamental elements of a laser system. The most obvious aperture is a window fabricated from a material transparent to the wavelength of interest. Besides being transparent, the material must exhibit mechanical properties sufficient to withstand the stresses resulting from the specific design installation, and must also be relatively inert with regard to the fluids in contact with the material surfaces. Actually all material appear to exhibit some absorption regardless of the wavelength of interest, although for some materials the absorption coefficient is quite small. Unfortunately, the materials with low absorption coefficients tend to have poor mechanical properties. Thus, windows for laser systems are fabricated from materials possessing a compromised combination of properties. For windows transmitting relatively low light flux densities, no problem results; however, for windows transmitting relatively high light flux densities, the absorption can be sufficient to either melt or cause thermal fracture of the window.
It would be desirable, if possible, to cool the fixed window so that a thermal failure will not occur. Unfortunately, this may not be sufficient since non-destructive thermal distortion can be sufficient to cause optical distortions which could be sufficient to seriously reduce optical qualities of the emitted light beam. Currently considered as a possible solution to the above problems is the use of an "aerodynamic window" which permits an unobstructed opening by maintaining the pressure between the two cavities at a required differential. This is accomplished by a shock wave established at the exit plane by a high flow rate of gas through a convergent/divergent nozzle. The obvious disadvantage of this solution is the energy needed to provide the gas flow requirements which is quite significant. For a usable laser aperture, an aerodynamic window would require the equivalent of 800hp.